linux-kernel - Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs saving

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Date:	Tue, 05 Jul 2011 18:21:28 -0400
From:	Valdis.Kletnieks@...edu
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Jan Beulich <JBeulich@...ell.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs saving

On Mon, 04 Jul 2011 15:22:23 +0200, Frederic Weisbecker said:
> On Mon, Jul 04, 2011 at 08:29:08AM +0100, Jan Beulich wrote:
> > >>> On 02.07.11 at 18:29, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > > The unwinder backlink in interrupt entry is very useless.
> > > It's actually not part of the stack frame chain and thus is
> > > never used.
> > 
> > I very much doubt this - see dump_trace()'s comment in its IRQ-stack
> > related code portion (and the corresponding use of irq_stack_end[-1]).
> > 
> > Jan
> 
> Good point. I misunderstood that.
> 
> But then I believe I accidentally fixed it back in
> "x86: Don't use frame pointer to save old stack on irq entry" by
> pushing %rsi instead in the new stack. It contains the backlink to
> the old stack.
> 
> If we keep the macro as-is, I'll add a comment to explain further
> what is involved there.

Ahh.. I was wondering why there wasn't suddenly a very lonely popq
out there... :)

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